Microwave transmission is greatly affected by weather. When the weather is fine, the transmission channel has high signal-to-noise ratio, and a higher modulation mode can be applied to the channel. To the contrary, during rainy and snowy days the signal-to-noise ratio of the transmission channel is decreased, and only a lower modulation mode can be applied to the channel with the same channel spacing. The function of such adaptive switching of modulation modes with variations in weather is referred to as adaptive code and modulation (ACM) switching.
Dynamic application of different modulation modes on the channel with the same channel spacing means that the bandwidth of the physical link varies with the circumstances of the weather, and, in order to enhance the utilization rate of the physical link, it is necessary for the frame structure of the multiplexed frame to also vary with variations of the link bandwidth. In the conventional art, the hybrid-multiplexing apparatus hybrid-multiplexes the data of various services to form multiplexed frames, and then sends them to the physical link for transmission. The frame structure of such a multiplexed frame is preset in accordance with such factors as the hybrid-multiplexing method and the attributes of the physical link, is invariant, and will not adaptively vary with variations of the bandwidth of the physical link. In other words, the conventional art hybrid-multiplexing method does not support ACM switching, and it is only possible to switch the frame structure of the multiplexed frame by using a method statically configured.
As the inventor of the present invention found during the process of research and practice about the conventional art, when the bandwidth of the physical link varies due to switching of modulation modes, use of the method of static configuration to switch the frame structure of the multiplexed frame would lead to service break during switching.